1. Field of the Invention
The invention relates in general to coordinate measurement machines (CMMs) and in particular to portable CMMs having an articulated arm.
2. Prior Art
Currently, portable articulated arms are provided as a measurement system with a host computer and applications software. The articulated arm is commonly used to measure points on an object and these measured points are compared to computer-aided design (CAD) data stored on the host computer to determine if the object is within the CAD specification. In other words, the CAD data is the reference data to which actual measurements made by the articulated arm are compared. The host computer may also contain applications software that guides the operator through the inspection process. For many situations involving complicated applications, this arrangement is appropriate since the user will observe the three-dimensional CAD data on the host computer while responding to complex commands in the applications software.
An example of a prior art portable CMM for use in the above-discussed measurement system is disclosed in U.S. Pat. No. 5,402,582 ('582), which is assigned to the assignee hereof and incorporated herein by reference. The '582 patent discloses a conventional three-dimensional measuring system composed of a manually operated multi-jointed articulated arm having a support base on one end thereof and a measurement probe at the other end. A host computer communicates to the arm via an intermediate controller or serial box. It will be appreciated that in the '582 patent, the arm will electronically communicate with the serial box which, in turn, electronically communicates with the host computer. Commonly assigned U.S. Pat. No. 5,611,147 ('147), which is again incorporated herein by reference, discloses a similar CMM having an articulated arm. In this patent, the articulated arm includes a number of important features including an additional rotational axis at the probe end thus providing for an arm with either a two-one-three or a two-two-three joint configuration (the latter case being a 7 axis arm) as well as improved pre-loaded bearing constructions for the bearings in the arm.
Still other relevant prior art CMMs include commonly assigned U.S. Pat. No. 5,926,782 ('782), which provides an articulated arm having lockable transfer housings for eliminating one or more degrees of freedom and U.S. Pat. No. 5,956,857 ('857) which provides an articulated arm having a quick disconnect mounting system.
More current portable CMMs of the type described herein do not necessitate the use of an intermediate controller or serial box since the functionality thereof is now incorporated in the software provided by the host computer. For example, commonly assigned U.S. Pat. No. 5,978,748 ('748), which is incorporated herein by reference, discloses an articulated arm having an on-board controller which stores one or more executable programs and which provides the user with instructions (e.g., inspection procedures) and stores the CAD data that serves as the reference data. In the '748 patent, a controller is mounted to the arm and runs the executable program which directs the user through a process such as an inspection procedure. In such a system, a host computer may be used to generate the executable program. The controller mounted to the arm is used to run the executable program but cannot be used to create executable programs or modify executable programs. By way of analogy to video gaming systems, the host computer serves as the platform for writing or modifying a video game and the arm mounted controller serves as the platform for playing a video game. The controller (e.g., player) cannot modify the executable program. As described in the '748 patent, this results in a lower cost three dimensional coordinate measurement system by eliminating the need for a host computer for each articulated arm. U.S. application Ser. No. 09/775,236 ('236), assigned to the assignee hereof and incorporated herein by reference, discloses a method and system for delivering executable programs to users of coordinate measurement systems of the type disclosed in the '748 patent. The method includes receiving a request to create an executable program from a customer and obtaining information related to the executable program. The executable program is then developed which guides an operator through a number of measurement steps to be performed with the three dimensional coordinate measuring system. The executable program is delivered to the customer, preferably over an on-line network such as the Internet.
Commonly assigned U.S. Pat. No. 6,131,299 ('299), (all the contents of which is incorporated herein by reference), discloses an articulated arm having a display device positioned thereon to allow an operator to have convenient display of positional data and system menu prompts. The display device includes for example, LEDs which indicate system power, transducer position status and error status. U.S. Pat. No. 6,219,928 ('928), which is assigned to the assignee and incorporated herein by reference, discloses a serial network for the articulated arm. The serial network communicates data from transducers located in the arm to a controller. Each transducer includes a transducer interface having a memory which stores transducer data. The controller serially addresses each memory and the data is transferred from the transducer interface memory to the controller. Commonly assigned U.S. Pat. No. 6,253,458 ('458) and U.S. Pat. No. 6,298,569 ('569) both disclose adjustable counter balance mechanisms for articulated arm portable CMMs of the type described herein.
While well suited for their intended purposes, there is a continued and perceived need in the industry for improved portable CMMs that are easier to use, more efficient to manufacture, provide improved features and can be sold at a lower cost.